Related papers: Axions and Cosmic Rays
Light bosonic fields may suffer an instability around a rotating compact object. This process, known as superradiance, leads to the exponential amplification of the field around a black hole or neutron star, while the spin of the central…
We establish a new covariant phenomenological model, which describes an influence of pseudoscalar (axion) field on spins of test massive particles. The model includes general relativistic equations of particle motion and spin evolution in…
We investigate the cosmological consequences of a simple theory in which the electric charge $e$ is allowed to vary. The theory is locally gauge and Lorentz invariant, and satisfies general covariance. We find that in this theory the fine…
We study the quantum propagation of particles in cosmological backgrounds, by considering a doublet of massive scalar fields propagating in an expanding universe, possibly filled with radiation. We focus on the dissipative effects related…
At finite density parity can be spontaneously broken in strong interactions with far reaching implications. In particular, a time-dependent pseudoscalar background would modify QED by adding a Chern-Simons term to the lagrangian. As a…
Relativistic axions are good candidates for the dark radiation for which there are mounting observational hints. The primordial decays of heavy fields produce axions which are ultra-energetic compared to thermalised matter and inelastic…
The origin of various celestial phenomena have remained mysterious for conventional astrophysics. Therefore, alternative solutions should be considered, taking into account the involvement of unstable dark-matter particle candidates, such…
The universe is filled with a diffuse and isotropic extragalactic background of gamma-ray radiation, containing roughly equal energy flux per decade in photon energy between 3 MeV-100 GeV. The origin of this background is one of the…
Searches for dispersive effects in the propagation of light at cosmological distances have been touted as sensitive probes of Lorentz invariance violation (LIV) and of theories of quantum gravity. Frequency-dependent time lags between…
Axions arise in many theoretical extensions of the Standard Model of particle physics, in particular the "string axiverse". If the axion masses, $m_a$, and (effective) decay constants, $f_a$, lie in specific ranges, then axions contribute…
We discuss spectral distortions, time delays and refraction of light in an axion or axion-plasma background. This involves solving the full set of geodesic equations associated to the system of Hamiltonian optics, allowing us to…
A cold relic axion condensate resulting from vacuum misalignment in the early universe oscillates with a frequency \sim m_a, where m_a is the axion mass. We summarize how the properties of photons propagating in such a medium are modified.…
We investigate the implications of energy-dependence of the speed of photons, one of the candidate effects of quantum-gravity theories that has been most studied recently, from the perspective of observations in different reference frames.…
We investigate the propagation of light through a plasma on a background Kerr spacetime via a Hamiltonian formulation. The behaviour of light when propagating through a vacuum and through a plasma is not the same; the convolution of…
A satisfactory theory of quantum gravity will very likely require modification of our classical perception of space-time, perhaps by giving it a 'foamy' structure at scales of order the Planck length. This is expected to modify the…
Axions seem ubiquitous in string theories and some of them may be produced non-thermally by heavy scalar decays, contributing to dark radiation. We study various cosmological effects of photons produced from the axionic dark radiation…
Motivated by different approaches to quantum gravity, one could consider that Lorentz invariance is not an exact symmetry of nature at all energy scales. Following this spirit, modified dispersion relations have been used to encapsulate…
This is an introductory review about the on-going search for a signal of Lorentz Invariance Violation (LIV) in cosmic rays. We first summarise basic aspects of cosmic rays, focusing on rays of ultra high energy (UHECRs). We discuss the…
In scalar-tensor theories with derivative interactions, backgrounds spontaneously break local Lorentz invariance. We study the motion of perturbations of the scalar, "phonons", on these anisotropic time-dependent backgrounds in curved…
We consider a cosmological scenario in which the very early Universe experienced a transient epoch of matter domination due to the formation of a large population of primordial black holes (PBHs) with masses $M \lesssim 10^{9}\,\textrm{g}$,…